Silane-based coating with a deodorizing effect for domestic appliances

ABSTRACT

Domestic appliances are provided with a catalytic deodorizing coating, prepared by applying a coating material containing a polycondensate of at least one hydrolysable organosilane, optionally one or more compounds of glass-forming elements, and particles of one or more catalytically active transition metal oxides, and then heat-treating the applied coating material.

The invention relates to domestic appliances comprising a catalyticcomposition for the purpose of deodorizing and oxidizing organiccomponents or carbon.

An object of the present invention is to provide catalytic compositionsfor domestic appliances which are capable of reducing or eliminatingenvironmental odour pollution (deodorizing) and which are able tooxidize organic components or carbon.

This objective is surprisingly achieved by means of domestic applianceshaving a catalytic composition which comprises a coating of a coatingmaterial on a support and is obtainable by applying the coatingmaterial, comprising (1) a polycondensate of

(A) one or more silanes of the general formula (I)

R_(a)—Si—X_((4-a))  (I)

in which the radicals R are identical or different and arenon-hydrolysable groups, the radicals X are identical or different andare hydrolysable groups or hydroxyl groups and a has the value 0, 1, 2or 3, with a being greater than 0 for at least 50 mol % of the silanes,or an oligomer derived therefrom,

(B) if desired, one or more compounds of glass-forming elements, and (2)particles of one or more transition metal oxides, the weight ratio oftransition metal oxide particles to polycondensate being from 10:1 to1:10, to the support and subjecting the applied coating material tothermal treatment, said catalytic composition representing a componentof said domestic appliance or of a device connected with said domesticappliance.

In the hydrolysable silanes (A), the hydrolysable groups X are, forexample, hydrogen or halogen (F, Cl, Br or I), alkoxy (preferably C₁₋₆alkoxy, such as methoxy, ethoxy, n-propoxy, i-propoxy and butoxy),aryloxy (preferably C₆₋₁₀ aryloxy, such as phenoxy), acyloxy (preferablyC₁₋₆ acyloxy, such as acetoxy or propionyloxy), alkylcarbonyl(preferably C₂₋₇ alkylcarbonyl, such as acetyl), amino, monoalkylaminoor dialkylamino having preferably from 1 to 12, in particular from 1 to6, carbon atoms.

The non-hydrolysable radicals R may be non-hydrolysable radicals R¹ ormay be radicals R² which carry a functional group, R¹ being preferred.

The non-hydrolysable radical R¹ is, for example, alkyl (preferably C₁₋₈alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl andt-butyl, pentyl, hexyl, octyl or cyclohexyl), alkenyl (preferably C₂₋₆alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl(preferably C₂₋₆ alkynyl, such as acetylenyl and propargyl) and aryl(preferably C₆₋₁₀ aryl, such as phenyl and naphthyl). The statedradicals R¹ and X may if desired have one or more customarysubstituents, such as halogen or alkoxy, for example.

Specific examples of the functional groups of the radical R² are theepoxy, hydroxyl, ether, amino, monoalkylamino, dialkylamino, amide,carboxyl, vinyl, acryloyloxy, methacryloyloxy, cyano, halogen, aldehyde,alkylcarbonyl, and phosphoric acid group. These functional groups areattached to the silicon atom via alkylene, alkenylene or arylenebridging groups, which may be interrupted by oxygen or —NH— groups. Thestated bridging groups are derived, for example, from the abovementionedalkyl, alkenyl or aryl radicals. The radicals R² contain preferably from1 to 18, in particular from 1 to 8, carbon atoms.

In one preferred embodiment, the silanes (A) comprise a mixture of

(A1) at least one hydrolysable silane of the general formula (II)

SiX₄  (II)

in which the radicals X are identical or different and are hydrolysablegroups or hydroxyl groups, or an oligomer derived therefrom, and

(A2) at least one organosilane of the general formula (III),

R ¹ _(a1) R ² _(a2)SiX_((4-a1-a2))  (III)

in which R¹ is identical or different at each occurrence and is anon-hydrolysable group, R² is identical or different at each occurrenceand is a radical which carries a functional group, X has the abovedefinition and a1 and a2 have the value 0, 1, 2 or 3, the sum (a1+a2)having the value 1, 2 or 3, or an oligomer derived therefrom in a molarratio (A1):(A2) of 5-50:50-95.

In the general formula (III), a1 preferably has the value 1 or 2, a2preferably has the value 0, 1 or 2 and the sum (a1+a2) preferably hasthe value 1 or 2.

Particularly preferred hydrolysable silanes (A) and (A1) aretetraalkoxysilanes such as tetraethoxysilane (TEOS). Particularlypreferred hydrolysable silanes (A) and (A2) are alkyltrialkoxysilanes,preferably containing C₁-C₈ alkyl, especially methyltriethoxysilane,aryltrialkoxysilanes, especially phenyltriethoxysilane,dialkyldialkoxysilanes, preferably containing C₁-C₈ alkyl, especiallydimethyldiethoxysilane, and diaryldialkoxysilanes, especiallydiphenyldiethoxysilane. Silanes containing functional groups (A) and(A2) are, for example, epoxy silanes such as3-glycidyloxypropyltrimethoxysilane (GPTS) and amino silanes such as3-aminopropyltriethoxysilane and3-(aminoethylamino)propyltriethoxysilane (DIAMO).

In the silane component (A) according to formula (I), a is greater than0 for at least 50 mol % of the silanes, i.e. at least 50 mol % of thesilanes contain at least one non-hydrolysable group R. The silanecomponent (A) preferably comprises from 50 to 95 mol % of silanes havingat least one non-hydrolysable group R. With regard to the formulae (II)and (III), the preferred molar ratio of the hydrolysable silane (A1) tothe organosilane (A2) in the polycondensate is 5 to 50:50 to 95,preferably from 1:1 to 1:6 and with particular preference from 1:3 to1:5. A particularly favourable molar ratio is 1:4.

The optional component (B) constitutes glass-forming elements which arepreferably dispersible or soluble in the reaction medium. It is possibleto use, for example, compounds (halides, alkoxides, carboxylates,chelates, etc.) of lithium, sodium, potassium, rubidium, caesium,beryllium, magnesium, calcium, strontium, barium, boron, aluminium,titanium, zirconium, tin, zinc or vanadium.

To prepare the polycondensate (1), the starting components (A) and,where appropriate, (B) are hydrolysed and condensed. The hydrolysis andcondensation are conducted either in the absence of a solvent or,preferably, in an aqueous or aqueous/organic reaction medium, whereappropriate in the presence of an acidic or basic condensation catalystsuch as HCl, HNO₃ or NH₃. The hydrolysis and condensation preferablytake place in the presence of an aqueous acid. The aqueous acids areused preferably in a concentration range of from 0.1 N to 10.0 N. Acidsused with preference are hydrochloric, nitric, phosphoric and aceticacid.

Additionally, during the preparation of the polycondensate, theinorganic particles set out below may be added. During the preparation,preferably, nanoscale inorganic particles, especially in the form of asol, are added. By way of example, silica sols may act as hydrolyticallyactive compounds in the sol. Suitable for this purpose are commerciallycustomary silica sols, such as the Levasils®, silica sols from Bayer AG,for example.

When a liquid reaction medium is used, the starting components aresoluble in the reaction medium. Particularly suitable organic solventsare water-miscible solvents, such as monohydric or polyhydric aliphaticalcohols, for example, but also aliphatic or aromatic hydrocarbons, suchas those having from 5 to 20 carbon atoms, ethers, esters, ketones,amides and alkylamides.

The hydrolysis and polycondensation preferably take place under theconditions of the sol-gel process, the reaction mixture being used inthe viscous sol state to coat the substrate.

Where appropriate, the hydrolysis and polycondensation are carried outin the presence of a complexing agent, examples of such agents beingnitrates, β-dicarbonyl compounds (e.g. acetylacetonates oracetoacetates), carboxylic acids (e.g. methacrylic acid) or carboxylates(e.g. acetate, citrate or glycolate), betaines, diols, diamines (e.g.DIAMO) or crown ethers.

The ratio of the hydrolytically active components to the hydrolysablesilanes (and, where appropriate, to the glass-forming elements) may becharacterized by the value R_(OR). The R_(OR) value represents the molarratio of water from the hydrolytically active components (water, aqueousacid, silica sol, etc.) to the abovementioned hydrolysable groups X fromthe silane components (and, where appropriate, the correspondinghydrolysable groups of the glass-forming elements). The sol obtainedpossesses, for example, an R_(OR) value of from 0.1 to 10 and preferablyfrom 0.2 to 2.

The polycondensate obtained is mixed, preferably in the form of a sol,with particles of one or more transition metal oxides, the ratio oftransition metal oxide particles to polycondensate being from 10:1 to1:10, preferably from 10:1 to 1:1 and with particular preference from10:1 to 2:1. In the case of this ratio, account is taken for thepolycondensate, with the exception of any other organic solvent, of thecomponents added for the purpose of preparing the polycondensate (inparticular the inorganic particles for preparing the condensate).

The average particle diameter of the transition metal oxides used issituated, for example, in a range from 10 nm to 20 μm. In the case ofcoated substrates which are to be used for improving odour, it ispreferred to use transition metal oxide particles having an averageparticle diameter of from 1 to 20 μm.

The particles consist substantially, or preferably completely, oftransition metal oxide. The transition metal oxide particles may becomposed of one transition metal oxide or of transition metal oxidemixtures. In the case of the transition metal oxide mixtures, which areused with preference, it is preferred to combine different transitionmetal oxide powders with one another so as to give particles comprisingdifferent transition metal oxides. It is of course also possible to useparticles which contain different transition metal oxides.

In the case of use for oxidation purposes in particular, however, it ispossible, besides the particles consisting essentially of transitionmetal oxides, to make additional use, in whole or in part, of particleswhich have the transition metal oxides indicated below at the surfacebut which otherwise are composed of a different material. In that casethe transition metal oxide particles are composed of particles of amaterial chosen preferably from one of the materials specified below forthe inorganic particles, said material being surface-coated with one ormore transition metal oxides. Preferably, these particles are coatedfully on the surface with the transition metal oxides. For the weightratio of transition metal oxide particles to polycondensate, theseparticles are taken into account as a whole as transition metal oxideparticles. The particles in question are in particular the particles inthe micrometre range, indicated below, which have been provided on thesurface, and/or impregnated, with transition metal oxides.

The transition metal oxides in question are, in particular,catalytically active transition metal oxides which have deodorizingand/or oxidizing properties. By transition metals are meant, as iscustomary, the elements of transition groups I to VIII of the PeriodicTable and the lanthanide and actinide elements. With particularpreference the transition metal oxide is selected from the oxides of themetals La, Ce, Ti, Zr, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag and Zn orfrom mixtures of these metal oxides. Preference is given to usingtransition metal oxide mixtures, with mixtures of the oxides of Mn andCe with one or two further transition metals, such as mixtures of theoxides of Mn/Co/Ce, Mn/Cu/Ce, Mn/Ni/Ce, Mn/Fe/Ce or Mn/Co/Ni/Ce, beingparticularly preferred. A further-preferred transition metal oxidemixture is a mixture of the oxides of Cu/V/La. It is also possible touse mixed oxides of the aforementioned transition metals.

In the transition metal oxide mixtures, the following amounts of thecorresponding metal oxides in the metal oxide mixture are preferred: Ce:1-70% by weight, V: 5-70% by weight, Mn: 20-95% by weight, Fe: 20-95% byweight, Co: 1-50% by weight, Ni: 1-50% by weight, Cu: 1-95% by weight.

Specific examples of transition metal oxides are MnO₂ (pyrolusite),γ-MnO₂, Co₃O₄, CO₂O₃, COO and CeO₂. It is of course also possible to useany other suitable transition metal oxide.

The BET surface area of the particles used is situated, for example,within a range from 1 to 100 m²/g.

Besides the transition metal oxide particles, cocatalysts may also beused in the coating material, in amounts for example of from 1 to 5% byweight, based on the transition metal oxide particles. Suitablecocatalysts are, for instance, K, Mg, Ca, Ba and Sr salts and also Aloxide and Sn oxide. Examples of suitable salts are the correspondinghalides, hydroxides, nitrates, carbonates, or phosphates. They may beadded, for example, by mixing the cocatalyst with the transition metaloxide particles or with the mixtures of the transition metal oxideparticles prior to addition to the polycondensate, or by separateaddition of the cocatalyst to the coating material. In the former case,it is preferred to use powders, and in the latter case it is preferredto use readily soluble salts of the cocatalyst.

The coating material may also include inorganic particles, which may beadded during the preparation of the polycondensate or of the coatingmaterial or thereafter. These particles may be nanoscale inorganicparticles or particles in the micrometre range. It is also possible toadd particles of both orders of magnitude, in which case the particlesin the micrometre range are employed in particular when the catalyticcomposition is used for oxidizing organic components or carbon.

The inorganic particles may be composed of any desired materials, withoxides being preferred. Preferred oxides are oxides of Si and Al(especially boehmite). The particles may be added, for example, in theform of powders or, especially the nanoscale particles, in the form ofsols.

The nanoscale inorganic particles preferably possess an average particlesize of up to 300 nm, in particular up to 100 nm and with particularpreference up to 50 nm. The particles may be added in colloidal form. Inthis case they can comprise sols or dispersible powders. Specificexamples of nanoscale inorganic particles are SiO₂, Al₂O₃, SnO₂, ironoxides or carbon (carbon black and graphite), especially SiO₂. Veryparticular preference is given to using silica sols as nanoscaleinorganic particles.

Especially if the catalytic compositions are to be used as oxidativecompositions, inorganic particles in the micrometre range may also beadded to the coating material. They serve to structure the coating andto produce cavities. These particles possess an average particlediameter of, for example, from 1 to 500 μm, preferably from 10 to 300μm. They are preferably oxide- and/or hydroxyl-containing compounds ofthe elements from main groups III and IV, such as aluminium oxides orsilicon oxides. They may have been activated. Examples that may bementioned include kieselguhr, alumina 90, silica gel 40 or silica gel60, produced by the company Merck.

Prior to their use, the abovementioned inorganic particles in themicrometre range may be impregnated with metal salts or mixtures ofmetal salts, such as chlorides, phosphates, formates, nitrates oracetates, and then treated at elevated temperatures in order to generatecatalytically active metal oxides on the surface. Preference is given tousing metal nitrates or metal acetates, since the anions form volatileproducts when treated within the temperature range used. Metals used arethe transition metals specified for the transition metal oxideparticles. In this case particles are obtained which are provided on thesurface with transition metal oxides, which are used in accordance withthe invention as transition metal oxide particles, and which are takeninto account as a whole for the weight ratio of transition metal oxideparticles to polycondensate.

The coating material may also comprise further additives. It ispossible, for example, to use additives suitable for adjusting viscosityand/or, in particular, for generating cavities during the thermaltreatment of the coating materials. For this purpose it is possible, forexample, to use customary thickeners. Specific examples are cellulosederivatives, such as hydroxypropylcellulose, starch, modified starch,polyvinyl alcohol and glycols, e.g. polyethylene glycol. Preference isgiven to using cellulose derivatives, especially hydroxypropylcellulose.In addition it is also possible to use the additives customary incatalytic compositions, such as pigments (e.g. black pigments).

The viscosity of the sol mixed with the transition metal oxide particlesmay also be adjusted, if desired, by removing or adding a solvent, e.g.one of those mentioned above. In this form, the sol is usually alsostorable for long periods. Where appropriate, it may be activated byadding water or aqueous acid, in which case the coating material ispreferably used within one month.

The coating material is applied to the support by customary coatingmethods. Applicable techniques are, for example, dipping, flow coating,spin coating, spraying or brushing.

Suitable supports are, for example, those of metals such as stainlesssteel, steel, copper, brass and aluminium; metal oxides, glasses such asfloat glass, borosilicate glass, lead crystal or silica glass; glassceramics, and ceramics such as Al₂O₃, ZrO₂, SiO₂ mixed oxides, or elseenamel, but also porous supports such as porous ceramics, for example.The shape of the supports is arbitrary. The supports in question may beplanar or structured. Particularly suitable supports are those in theform of meshes, honeycombs or nets, such as wire meshes, examples beingsteel wire meshes, ceramic honeycombs or wire nets.

The supports may be pretreated prior to the application of the coatingmaterial. For example, they are subjected to cleaning, usingcommercially customary alkaline cleaners, for example. It is likewisepossible, for example, by heat-treating steel supports and formingchromium oxide whiskers on the surface, to bring about substantiallyimproved adhesion of the coating material to steel supports.

The resulting coating is subjected to initial drying, if desired, andthen heat-treated. This can be done at temperatures of from 200° C. to700° C., preferably from 300° C. to 400° C. The heat treatment may becarried out in air on in an inert gas such as nitrogen or argon. Theheat treatment may also take place if desired by means of IR or laserradiation. The heat treatment may be accompanied, for example, bydrying, curing or consolidation or compaction of the coating material.

The coating operation is preferably performed so as to give coatthicknesses of from 0.01 to 500 μm, preferably from 1 to 500 μm. Wherethe catalytic compositions are used for the purpose of deodorizing, coatthicknesses of from 30 to 100 μm, in particular from 25 to 75 μm, arepreferred. Where the catalytic compositions are used as oxidativelyactive surfaces, coat thicknesses of from 1 to 10 μm are suitable whenusing transition metal oxides having an average particle size of lessthan 200 nm. The catalytic compositions which serve as oxidativelyactive surfaces, and which additionally comprise inorganic particles inthe micrometre range, preferably have coat thicknesses of from 100 to400 μm.

The catalytic compositions of the invention may have a porous or anon-porous coating. Preferably, the catalytic compositions have porouscoatings. The pores may comprise microscopically visible cavities on thesurface and/or relatively fine micropores. The cavities visible on thesurface under the microscope have an approximately globular morphology(hemispheres) and their diameter is from about 1 to 5 μm. Their extentand form in the interior of the coat cannot be determined by microscopy.The determination of the BET surface areas of preferred embodimentsindicates that relatively fine micropores are present thereinalternatively or additionally.

The catalytic composition of the invention has a deodorizing effect; inother words, odour pollution caused by substances can be reduced oravoided completely. The deodorizing activity is found in particular attemperatures above 150° C., for example at temperatures from 150 to 500°C., preferably from 200 to 350° C. The odour-polluted air is guided pastthe catalytic composition at elevated temperatures. As it passes,substances present in the air are degraded.

The catalytic composition is also capable of oxidizing organiccomponents or carbon, such as carbon black or graphite, which arepresent, for example, on the surface of the catalytic composition. Theoxidizing activity is found in particular at the temperature rangesindicated above.

The catalytic compositions are preferably used for these purposes insuch a way that they are located directly on any surface of the domesticappliance in question, in which case this surface acts as the substrate,or they represent a component of an additional device, connected wherenecessary via a connecting line, within or in the vicinity of thedomestic appliance. The surface of the domestic appliance may, forinstance, be part of the casing or an inner wall, preferably formed ofmetal. The additional device may, for instance, be an exhaust means ofthe domestic appliance. In addition to the catalytic composition, theadditional device may e.g. comprise heating and venting means.

In this manner, the invention provides a simple way to combat malodorsor surface staining which may occur in households and domesticappliances. Domestic appliances in accordance with the present inventionare all articles and devices normally used in households. Suitableexamples are stoves, stove-tops, kitchen vents and deep-fat fryers.Preferred field of application are electrical and gas stoves, kitchenvents and/or deep-fat fryers.

EXAMPLES A. Preparation of the Silane Sols

Silane sol 1: MTKS sol, R_(OR)=0.4

A mixture of 1069.86 g (6.0 mol) of methyltriethoxysilane and 312.48 g(1.5 mol) of tetraethoxysilane is divided into two portions (portion 1and portion 2) of equal weight.

To portion 1, 246.84 g of silica sol (Levasil 300/30, aqueous, basic,Bayer AG) are added with thorough stirring. After an emulsion has formed(about 30 s), 5.60 g of 36% strength by weight HCl are added. Afterbrief stirring (30-50 s) the reaction mixture becomes clear withheating. Portion 2 is added quickly and all at once to this reactionmixture. After a short time, the reaction mixture becomes cloudy owingto a colourless precipitate (NaCl). This is followed by stirring withcooling in an ice bath for 15 minutes. The silane hydrolysate is left tostand at room temperature for 12 h and decanted from the sedimentedsolid, thus giving the ready-to-use MTKS sol.

Silane sol 2: MDKS sol, ROR=0.2

35.10 g of silica sol (Levasil 300/30, aqueous, basic, Bayer AG) and1.10 g of 36% strength by weight HCl are added simultaneously to amixture of 356.62 g (2.0 mol) of methyltriethoxysilane and 74.14 g (0.5mol) of dimethyldiethoxysilane, with thorough stirring. After briefstirring (30-50 s) the reaction mixture becomes clear with heating.After a short time, the reaction mixture becomes cloudy owing to acolourless precipitate (NaCl). This is followed by stirring with coolingin an ice bath for 15 minutes. The silane hydrolysate is left to standat room temperature for 12 h and decanted from the sedimented solid,thereby giving the ready-to-use MDKS sol.

Silane sol 3: MPTKS sol, ROR=0.4

3.29 g of silica sol (Levasil 300/30, aqueous, basic, Bayer AG) and 0.13g of 36% strength by weight HCl are added simultaneously to a mixture of11.59 g (0.065 mol.) of methyltriethoxysilane, 3.61 g (0.015 mol) ofphenyltriethoxysilane and 4.17 g (0.020 mol) of tetraethoxysilane, withthorough stirring. After brief stirring (30-50 s) the reaction mixturebecomes clear with heating. After a short time, the reaction mixturebecomes cloudy owing to a colourless precipitate (NaCl). This isfollowed by stirring with cooling in an ice bath for 15 minutes. Thesilane hydrolysate is left to stand at room temperature for 12 h anddecanted from the sedimented solid, thereby giving the ready-to-useMPTKS sol.

Silane sol 4: MPrTKS sol, ROR=0.4

7.00 g of silica sol (Levasil 300/30, aqueous, basic, Bayer AG) and 0.23g of 32% strength by weight HCl are added simultaneously to a mixture of15.00 g (0.084 mol) of methyltriethoxysilane, 14.95 g (0.091 mol) ofn-propyltrimethoxysilane and 8.96 g (0.043 mol) of tetraethoxysilane,with thorough stirring. After brief stirring (30-50 s) the reactionmixture becomes clear with heating. After a short time, the reactionmixture becomes cloudy owing to a colourless precipitate (NaCl). This isfollowed by stirring with cooling in an ice bath for 15 minutes. Thesilane hydrolysate is left to stand at room temperature for 12 h anddecanted from the sedimented solid, thereby giving the ready-to-useMPrTKS sol.

Silane sol 5: MD sol, ROR=0.4

5.04 g of 0.1 N HCl are added to a mixture of 35.66 g (0.2 mol) ofmethyltriethoxysilane and 7.41 g (0.05 mol) of dimethyldiethoxysilane,with thorough stirring. After brief stirring (30-50 s) the reactionmixture becomes clear with heating. The silane hydrolysate is left tostand at room temperature for 12 h, thereby giving the ready-to-use MDsol.

B. Preparation of the Catalyst Mixtures

The catalyst mixtures used are mixtures of commercial transition metaloxide powders from Ferro or Aldrich:

MnO₂: Powder from Ferro, predominantly MnO₂ (pyrolusite), with a littleγ-MnO₂ and a little MnO₂

Co_(y)O_(x): Powder from Ferro, predominantly Co₃O₄, with a very littleCoO

Catalyst Mixture 1: Mn/Co/Ce

Catalyst mixture 1 is prepared by intimately mixing 800.00 g of MnO₂,100.00 g of Co_(y)O_(x) and 100.00 g of CeO₂.

Catalyst Mixture 2: Mn/Co/Ce

Catalyst mixture 2 is prepared by intimately mixing 800.00 g of MnO₂,150.00 g of Co_(y)O_(x) and 50.00 g of CeO₂.

Catalyst Mixture 3: Mn/Cu/Ce

Catalyst mixture 3 is prepared by intimately mixing 650.00 g of MnO₂,300.00 g of Cu₂O and 50.00 g of CeO₂.

Catalyst Mixture 4: Mn/Co/Ni/Ce

Catalyst mixture 4 is prepared by intimately mixing 700.00 g of MnO₂,100.00 g of Co_(y)O_(x), 150.00 g of NiO and 50.00. g of CeO₂.

C. Preparation of the Coating Materials Example 1

1000.00 g of catalyst mixture 1 are stirred at room temperature for 2 hwith 300.00 g of silane sol 1 and 233.33 g of ethanol. Then 32.35 g of10% strength by weight aqueous hydrochloric acid are added foractivation (increasing the R_(OR) value from 0.4 to 0.8), the mixture isstirred at room temperature for at least 2 h, and the ready-to-usecoating suspension is obtained.

Example 2

1000.00 g of catalyst mixture 2 are stirred at room temperature for 2 hwith 200.00 g of silane sol 1 and 350.00 g of ethanol. Then 23.49 g of10% strength by weight aqueous hydrochloric acid are added foractivation (increasing the R_(OR) value from 0.4 to 0.8), the mixture isstirred at room temperature for at least 2 h, and the ready-to-usecoating suspension is obtained.

Example 3

1000.00 g of catalyst mixture 3 are stirred at room temperature for 1 hwith 400.00 g of silane sol 2 and 185.00 g of ethanol. Then 47.97 g of10% strength by weight aqueous hydrochloric acid are added foractivation (increasing the R_(OR) value from 0.2 to 0.6), the mixture isstirred at room temperature for at least 4 h, and the ready-to-usecoating suspension is obtained.

Example 4

1000.00 g of catalyst mixture 3 are stirred at room temperature for 1 hwith 18.00 g of silane sol 3 and 25.00 g of ethanol. Then 1.52 g of 10%strength by weight aqueous hydrochloric acid are added for activation(increasing the R_(OR) value from 0.4 to 0.7), the mixture is stirred atroom temperature for at least 2 h, and the ready-to-use coatingsuspension is obtained.

Example 5

1000.00 g of catalyst mixture 4 are stirred at room temperature for 1 hwith 40.00 g of silane sol 5 and 11.00 g of ethanol. Then 4.66 g of 10%strength by weight aqueous hydrochloric acid are added for activation(increasing the R_(OR) value from 0.4 to 0.8), the mixture is stirred atroom temperature for at least 2 h, and the ready-to-use coatingsuspension is obtained.

D. Coating and Heat Treatment (Especially for Deodorizing Purposes)

The support material used is steel wire mesh (diameter about 5 cm,height about 1 cm) or ceramic honeycombs. the steel meshes are first ofall degreased using a commercial alkaline cleaner and then rinsedthoroughly with deionized water, before being dried at room temperature.The dry steel meshes are subsequently treated at 500° C. for 1 h.

Coating takes place by impregnating the steel wire meshes or the ceramichoneycombs in one of the coating materials (coating suspensions)described in section C. The excess coating suspension is removed byblowing with compressed air. After drying at room temperature (2 h), thecoating is solidified by heat treatment. For this purpose the coatedsupports are heated from room temperature to 300-400° C. over the courseof 1 h, held at 300-400° C. for 1 h, and then cooled to room temperatureover 6 h.

Alternatively, the heat treatment may also be effected by directplacement of the dried, coated supports into an oven preheated to300-400° C. and rapid cooling of the hot supports to room temperatureover a few minutes.

The thicknesses of the thermally solidified coats are typically in therange 25-75 μm. The coat thicknesses may be set, for example, on the onehand by way of the viscosity of the coating suspension (which can beadjusted, for example, by adding an appropriate amount of ethanol), onthe other by way of the pressure of the compressed air or the time ofaction of the compressed air during removal of the excess coatingsuspension.

E. Catalytic Composition 1 (Especially for Oxidizing)

E.1 Preparation of an Mn/Cu/Ce Catalyst on Alumina Particles

40.47 g (0.141 mol) of Mn(NO₂)₂•6 H₂O, 11.63 g (0.050 mol) of Cu(NO₃)₂•3H₂O and 15.20 g (0.035 mol) of Ce(NO₃) _(3•6) H₂O are dissolved in amixture of 30.00 g of ethanol and 30.00 g of water at 50C. 100.00 g ofalumina 90 (active, acidic (alternatively, neutral or basic can also beused), particle size 63-200 μm, from Merck) are added to this solutionand the solvent mixture is evaporated off with stirring at 50-70° C. for3 h. The alumina impregnated with the metal nitrates is subsequentlytreated at 500° C. for 1 h. Analogously, it is also possible to use thecorresponding molar amounts of metal acetates or, instead of aluminium90, the further Merck products silica gel 40, particle size 63-200 μm.silica gel 60, particle size 63-200 μm, or kieselguhr, particles sizeapproximately 100 μm.

E.2 Coating Material

150.00 g of the above-described Mn/Cu/Ce catalyst (E.1) on the aluminaparticles are intimately mixed with 50.00 g of catalyst mixture 1.100.00 g of a 5% strength by weight solution of hydroxypropylcellulosein ethanol are added with stirring to this mixture. 140.00 g of silanesol 2 are activated (increasing the R_(OR) value from 0.2 to 0.8) byaddition of 22.67 g (1.26 mol) of water, with stirring, and the mixtureis stirred at room temperature for 30 minutes. The activated MDKS sol isadded to the above-described mixture of Mn/Cu/Ce catalyst, catalystmixture 1 and hydroxypropylcellulose in ethanol, at room temperaturewith stirring, and the mixture is then stirred at room temperature for15 minutes to give the ready-to-use coating material.

E.3 Coating and Thermal Solidification

The support material used is steel substrates (metal panels 10×10 cm).The steel substrates are first of all degreased using a commercialalkaline cleaner, then rinsed thoroughly with deionized water, andsubsequently dried at room temperature. The dry steel substrates maythen be treated at 500° C. for 1 h.

The cleaned, or cleaned and heat-treated, steel substrates are floodedwith the coating material. The coated steel substrates are dried at roomtemperature for 1 h, then heated from room temperature to 500° C. over 1h, held at. 500° C. for 1 h, and then cooled to room temperature over 6h.

The thicknesses of the thermally solidified coats are typically in therange 150-400 μm, depending on the support material used and the amountof coating material used.

F. Evaluation

Method of Determining the Deodorizing Activity

About 100 mg of the following test substances are introduced into acirculating-air oven preheated to 300° C. (catalyst temperature about300° C., support: steel wire mesh):

pyrazine, thiazole, maltol, vanillin and 2,4-decadienal.

The test substances evaporate in the hot oven, with the vapours beingpassed as off-gases (off-gas flow: 0.5-1.2 l/s) by the stream ofcirculating air through an outlet port without a catalyst and an outletport with catalyst to a downstream sample collector. The collectedsamples are analysed by means of GC-MS spectroscopy. The spectra areused to determine breakdown rates for the test substances in the off-gasstream that passes over the catalyst in comparison to the off-gas streamwhich does not pass over a catalyst (principle: relative measurement onan experimental system). The breakdown rates are indicated below in %.

Catalyst Pyrazine Thiazole Maltol Vanillin Decadienal Pd/Pt  0  0 90 90— cat (*1) (*2) 83 88 73 78 65 (*3) 69 56 74 70 — (*1): Palladium,metallic, on steel wire nets, commercial catalyst (*2): InventiveMn/Co/Ce-MTKS sol cat., coating material of Example 1 (*3): InventiveMn/Cu/Ce-MDKS sol cat., coating material of Example 3.

It is found that the catalytic compositions of the invention are capableof breaking down not only the other test substances but alsoheterocycles such as pyrazine and thiazole. This is not possible withcommercially customary palladium catalysts. Also, with the catalyticcompositions of the invention, there is no loss of catalytic activityafter ten test cycles. In contrast, the commercially customary palladiumcatalyst is poisoned by heterocycles such as thiazole, losing catalyticactivity with time.

Evaluation of the Oxidizing Capacity

[Test method according to DIN 51 171, “Testing of the self-cleaningcapacity of continuously self-cleaning enamel coatings”]

Defined amounts (in each case 20-25 mg) of soya oil or engine oil areapplied dropwise to the samples under investigation, at five pointslocated on a circle, and after each dropwise addition are burnt by aone-hour heat treatment at 250° C., until a visible lustre appears as aresult of the accumulation of unburned residues. The number of cyclesuntil lustre occurs is used for the assessment.

Coating Oil Number of cycles to lustre (*1) Soya 4-5 (*2) Soya 15-17(*3) Soya 13-15 (*1): Commercially customary, oxidative enamel,containing Fe/Mn oxides (*2): Catalytic composition 1 (*3): Catalyticcomposition 1, but using silica gel 40 as support material instead ofalumina 90

The catalytic compositions of the invention (coat thicknesses between150-400 micrometres) possess high absorbency, owing to the cavitieswhich exist in the coating, and hence have a good spreading capacity foroils. In contrast, the glass-like enamels have a low absorbency andspreading capacity.

We claim:
 1. A domestic appliance comprising a catalytic composition fordeodorizing or oxidizing purposes, the catalytic composition comprisinga coating of a coating material containing particles of at least onecatalytically active transition metal oxdie on a support, prepared by aprocess comprising the steps of: (i) applying to the support a coatingmaterial comprising: (1) a polycondensate of (A) at least one silane ofthe formula R_(a)—Si—X_((4-a)) where each R, which may be the same ordifferent, is a non-hydrolyzable group; each X, which may be the same ordifferent, is a hydroxy group or hydrolyzable group; and a is an integerof 0 to 3 and is greater than 0 for at least 50 mol % of the silanes; oran oligomer derived therefrom, and (B) optionally, at least one compoundof a glass-forming element, and (2) particles of at least onecatalytically active transition metal oxide, the weight ratio of theparticles of the at least one catalytically active transition metaloxide to the polycondensate being from 10:1 to 1:10; and (ii) thermallytreating the applied coating material to form the coating, the catalyticcomposition being a component of the domestic appliance or of a deviceconnected to the domestic appliance.
 2. A domestic appliance of claim 1where a is greater than 0 for between 50 mol % and 95 mol % of thesilanes.
 3. A domestic appliance of claim 1 where the at least onetransition metal oxide is selected from the oxides of the metals La, Ce,Ti, Zr, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag and Zn, and mixturesthereof.
 4. A domestic appliance of claim 1, where the particles of theat least one transition metal oxide have a diameter between 10 nm and 20μm.
 5. A domestic appliance of claim 1 where the coating has a thicknessbetween 0.01 μm and 500 μm.
 6. A domestic appliance of claim 1 where thesupport is composed of metal, metal oxide, glass, glass ceramic, ceramicor porous material.
 7. A domestic appliance of claim 1 where the thermaltreatment of step. (ii) occurs at between 200 ° C. and 700 ° C.
 8. Adomestic appliance of claim 1 where the coating material also comprisesinorganic particles.
 9. A domestic appliance of claim 1 where thecoating is porous.